1. Field of the Invention
The invention relates to a method and a contrivance for the breaking-up of a fresh and hot coke batch in a receiving container with movable plate segments, with the coke batch being transported in the receiving container of a flat-bed transfer car to a quenching tower, where the coke batch is cooled down to ambient temperatures by using movable plate segments so that the coke structure loosens up and gap-like cavities form in the compacted coke batch, and on account of these gap-like cavities an increased amount of water can flow into the inside of the coke batch during the subsequent quenching process, the reduced quenching time and the lower water consumption for coke quenching resulting in a higher economic efficiency of the method, a higher coke quality and a lower emission load for the environment. The invention also relates to a contrivance for applying this method.
2. Description of the Related Art
Conventional horizontal-type coke-oven chambers are equipped with so-called coke transfer machines on the coke side of the coke-oven batteries, such machines being used for operations to be performed in connection with the coke-sided pushing of the carbonised coke. Normally the coke quenching device is a quenching car which can be—at least partly—moved separately underneath the coke transfer machine. The quenching car typically includes a receiving container which takes up the coke from the coke-oven chamber and takes it to the quenching tower. Between the receiving container and the coke-oven chamber there is frequently a coke transfer machine which, in a simple case, may consist of a wharf or a sloped plate and ensures, by integral suction devices, that the emissions produced when the coke drops out of the oven are evacuated into a dust extraction system, thereby minimising the environmental load. The quenching car typically travels on rails and can be moved directly below the quenching tower by means of a transport device. The quenching tower is a wet-quenching tower according to an embodiment frequently used but it can also be a dry-quenching tower.
The coal-to-coke carbonisation is frequently carried out in so-called heat-recovery or non-recovery-type coke-oven chambers. Modern coke ovens of the heat-recovery or non-recovery-type are not equipped with such extracting transfer machines. After carbonisation, the coke is here pushed into a flat-bed quenching car which is on the same level as the lower edge of the oven, thereby avoiding the production of emissions when pushing the coke, as the coke cake does not drop vertically out of the oven.
In the practice of coke-oven engineering, the coke is considered fully carbonised if the content of volatile components is below 1.8 weight percent (wt.-%). These volatile residual components are distributed heterogeneously inside the coke batch and normally burn if they are exposed to an oxygen-bearing ambient atmosphere. The coke is normally pushed into this quenching car at average temperatures between 900 and 1100° C. When pushing has been completed, the quenching car is moved to the quenching tower. In the quenching tower the coke is then cooled to temperatures of approx. 100° C. by supplying water.
A typical contrivance including a quenching car for wet quenching is described in DE 1253669 B. The invention relates to a contrivance for the quenching of coke that has been discharged from horizontal coking chambers, the contrivance consisting of a stationary quenching compartment with stack-like part and travelling along the oven battery on the coke side or being supplied from a receiving car or from a receiving car for glowing coke, and a coke receiving compartment which is followed by a circulating conveying grid with spraying system on top, in which tube bundles containing heatable process fluid are installed above the conveying grid between the device for controlling the height of the coke layer and the spraying system, these tube bundles possibly communicating with the known tube bundles of the coke receiving compartment. Embodiments of a quenching car and its control system are disclosed by WO 2006/089612 A1, U.S. Pat. No. 5,564,340 A and EP 964049 A2.
There are also embodiments where the coke is quenched from below by supplying water. Such embodiment is also called “bottom quenching”. It is also common practice to combine both quenching methods. Typical embodiments of a dry quenching method are disclosed by WO 91/09094 A1 and EP 0084786 B1.
Transport of the coke can be carried out in quenching cars of the flat-bed type or quenching cars with receiving container. Flat-bed quenching cars are described in CN 2668641 Y, for example. Quenching cars with receiving container are described in U.S. Pat. No. 5,564,340 A, for example. The coke does not burn at first, as an ash layer of up to 30 mm forms at the upper edge of the coal batch by combustion of the uppermost coal layers during the first hours of the carbonisation process due to direct heating. This ash layer largely protects the coke from further combustion during transport to the quenching tower. In this way the emissions remain within tolerable limits and can be sucked off during the transport by suitable extraction devices if required.
Coke quenching systems have normally been designed assuming that coke densities are between 400 and 600 kg*m−3 and the vertical height of the coke cake is approx. 1000 mm. To improve the economic efficiency, the initial coal densities of 850 to 1200 kg*m−3 have recently been raised. The coke cake densities obtained from carbonisation are therefore above the known range of 400 to 600 kg*m−3 and also cause sealing of the coke cake surface. The result is that the quenching water cannot penetrate vertically into the batch or only with delay.
The coke is then quenched in the quenching tower. The high degree of compaction of the coal cake and of the coal cake obtained from carbonisation makes it impossible for the quenching water to penetrate vertically into the batch or only with delay. In this way the cooling effect is retarded.
An additional impedance to the effective cooling of the fresh coke batch is the so-called “Leidenfrost effect”. As the temperature of the coke batch is high, the water impinging on the surface of the hot coke will evaporate instantaneously. As a result a coat of water vapour forms around the coke pieces preventing the entry of further water. The water impinging on the surface of the coke forms a protective vaporous coat for a limited period of time and protects the coke from direct heat transfer. In this way the water cannot penetrate efficiently into the inside of the coke and therefore flows off laterally not reaching the inner coke layers.
In this way the quenching water is distributed unevenly across the entire volume of the coke batch. As this also results in uneven cooling by the quenching water, the temperature distribution across the coke batch will likewise be uneven. Hence there will still be parts of the coke cake after quenching that show a coke temperature of more than 100° C. This is a significant problem when processing and using the coke downstream as coke batch portions of temperatures above 100° C. can damage transport and conveying belts which are frequently made of hard rubber or plastics. The quenched coke will thus also consist of partial batches the water content of which is above 3 wt.-%. An elevated water content of more than 3 wt.-% in the coke is also a problem as the water will diminish the product quality of the raw iron in the downstream blast-furnace process.
The aim in the processes of pushing and quenching of produced coke cakes is to reduce the emissions or to eliminate them as completely as possible. The emissions can be reduced by transporting the coke cake to the quenching tower after the end of the pushing process without any further mechanical treatment. The ash layer produced by the combustion of the uppermost coal layers largely protects the coke from further combustion during transport to the quenching tower and does not produce any emissions unless it is whirled up.